seriesDefaults.legendItem.markers.type String|Function
The markers shape.
The supported values are:
- "circle" - the marker shape is circle.
- "square" - the marker shape is square.
- "triangle" - the marker shape is triangle.
- "cross" - the marker shape is cross.
- "rect" - alias for "square".
- "roundedRect" - the marker shape is a rounded rectangle.